In a liquid chromatograph, a sample is pressurized together with a liquid used as a mobile phase and sent to a column. Components of the sample are separated in the column, eluted, and then detected by a detector. A typical liquid chromatograph includes a mobile phase reservoir for holding a liquid used as a mobile phase, a mobile phase deaerator for removing air from the liquid mobile phase, a pump for feeding the liquid mobile phase from the mobile phase reservoir to a detector, a sample injection device for injecting a sample into the liquid mobile phase being sent to a separation column, the separation column filled with a filler for separating components of the sample, a constant-temperature bath for maintaining the separation column at a substantially constant temperature, and a detector for detecting eluted components of the sample.
A sample injection device of a liquid chromatograph has a switching valve, for example, as disclosed in patent document 1. The disclosed switching valve is configured to allow a sample to be drawn into a sample injection needle when drawing the sample into the sample injection needle and to allow the sample drawn into the sample injection needle to be sent to a column along with a flow of a mobile phase when the sample injection needle is attached to a sample injection port. FIG. 1 is a drawing illustrating an exemplary sample injection device.
The exemplary sample injection device shown in FIG. 1 includes a sample injection needle 100 (100A through 100C), a pump 103, a syringe 111, a wash liquid pump 112, a valve 113, a sample container 114, an injection valve (switching valve) 115, a cleaning device 120, a sample injection port 124, and a needle moving unit (not shown).
The injection valve 115 has six ports to which the sample injection needle 100, the mobile phase pump 103, the valve 113, the cleaning device 120, and the sample injection port 124 are connected. The injection valve 115 switches between a connection mode (connection mode A) indicated by solid lines A in FIG. 1 and a connection mode (connection mode B) indicated by broken lines B in FIG. 1.
Before analysis of a sample is started, the injection valve 115 is in the connection mode A and the sample injection needle 100 is attached to the sample injection port 124 (the sample injection needle 100 in this position is indicated by the reference number 100A) The sample injection needle 100A is connected via the injection valve 115 to the pump 103. The sample injection port 124 is connected via piping 125 and the injection valve 115 to a separation column 105. Accordingly, in the connection mode A, a mobile phase supplied from the pump 103 is fed into the separation column 105 via the sample injection needle 100A, the sample injection port 124, the piping 125, and the injection valve 115.
On the other hand, when drawing a sample into the sample injection needle 100, the injection valve 115 is switched to the connection mode B and the sample injection needle 100 is inserted into the sample container 114 (the sample injection needle 100 in this position is indicated by the reference number 100B). In the connection mode B, the sample injection needle 100B is connected to the syringe 111 via the injection valve 115 and the valve 113. Therefore, the sample in the sample container 114 can be drawn into the sample injection needle 100B by operating the syringe 111. Also, in the connection mode B, the pump 103 is connected via the injection valve 115 to the separation column 105 and therefore the mobile phase continues to be supplied to the separation column 105 even when the sample is being drawn into the sample injection needle 100.
When feeding the sample drawn into the sample injection needle 100 to the separation column 105, the sample injection needle 100 is inserted into a cleaning unit 117B and then into a cleaning unit 117A of the cleaning device 120 to clean its outer surface. New supplies of a wash liquid are continuously supplied to the cleaning units 117A and 117B of the cleaning device 120 by connecting the valve 113 to the wash liquid pump 112 at specified timings. Excess wash liquid is discharged from a waste liquid port 123.
Then, the cleaned sample injection needle 100 is inserted into the sample injection port 124 and the injection valve 115 is switched again to the connection mode A. As a result, the mobile phase supplied from the pump 103 to the sample injection needle 100A pushes the sample out of the sample injection needle 100A into the sample injection port 124. The sample is then carried by the flow of the mobile phase via the piping 125 and the injection valve 115 to the separation column 105. Thus, in the conventional sample injection device, a sample is sent from the sample injection needle 100A to the separation column 105 through the injection valve 115.
[Patent document 1] Japanese Patent Application Publication No. 10-010103